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UseConsistentParameterSetName

Severity Level: Warning

Description

This rule detects inconsistent parameter set naming and configuration issues that can cause runtime errors. Parameter set names in PowerShell are case-sensitive, unlike most other PowerShell elements. With this rule enabled, it's easier to debug your functions. This rule is disabled by default.

This rule performs five different checks:

  1. Missing DefaultParameterSetName - Warns when parameter sets are used but no default is specified.
  2. Multiple parameter declarations - Detects when a parameter is declared multiple times in the same parameter set. This issue becomes a runtime exception, so this check catches it earlier.
  3. Case mismatch between DefaultParameterSetName and ParameterSetName - Ensures consistent casing.
  4. Case mismatch between different ParameterSetName values - Ensures all references to the same parameter set use identical casing.
  5. Parameter set names containing newlines - Warns against using newline characters in parameter set names.

Guidance

  • Use a DefaultParameterSetName when defining multiple parameter sets
  • Ensure consistent casing between DefaultParameterSetName and ParameterSetName values
  • Use identical casing for all references to the same parameter set name
  • Avoid declaring the same parameter multiple times in a single parameter set
  • Don't use newline characters in parameter set names

Notes

  • The first occurrence of a parameter set name in your code is treated as the canonical casing
  • Parameters without [Parameter()] attributes are automatically part of all parameter sets
  • It's a PowerShell best practice to always specify a DefaultParameterSetName when you're using parameter sets

Example

Noncompliant

# Missing DefaultParameterSetName
function Get-Data {
    [CmdletBinding()]
    param(
        [Parameter(ParameterSetName='ByName')]
        [string]$Name,

        [Parameter(ParameterSetName='ByID')]
        [int]$ID
    )
}

# Case mismatch between DefaultParameterSetName and ParameterSetName
function Get-Data {
    [CmdletBinding(DefaultParameterSetName='ByName')]
    param(
        [Parameter(ParameterSetName='byname')]
        [string]$Name,

        [Parameter(ParameterSetName='ByID')]
        [int]$ID
    )
}

# Inconsistent casing between ParameterSetName values
function Get-Data {
    [CmdletBinding(DefaultParameterSetName='ByName')]
    param(
        [Parameter(ParameterSetName='ByName')]
        [string]$Name,

        [Parameter(ParameterSetName='byname')]
        [string]$DisplayName
    )
}

# Multiple parameter declarations in same set
function Get-Data {
    param(
        [Parameter(ParameterSetName='ByName')]
        [Parameter(ParameterSetName='ByName')]
        [string]$Name
    )
}

# Parameter set name with newline
function Get-Data {
    param(
        [Parameter(ParameterSetName="Set`nOne")]
        [string]$Name
    )
}

Compliant

# Proper parameter set configuration
function Get-Data {
    [CmdletBinding(DefaultParameterSetName='ByName')]
    param(
        [Parameter(ParameterSetName='ByName', Mandatory)]
        [string]$Name,

        [Parameter(ParameterSetName='ByName')]
        [Parameter(ParameterSetName='ByID')]
        [string]$ComputerName,

        [Parameter(ParameterSetName='ByID', Mandatory)]
        [int]$ID
    )
}

Configuration

Rules = @{
    PSUseConsistentParameterSetName  = @{
        Enable = $true
    }
}

Parameters

Enable

This parameter controls whether ScriptAnalyzer checks the code against this rule. It accepts a boolean value. To enable this rule, set this parameter to $true. The default value is $false.

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